Artificial lifts system having downhole pumps are widely used in wells to lift liquid produced in the well to the surface. To reduce wear, plugging, and other issues from sand and other solid particles, the intake of the downhole pumps can be fitted with a sand control system. For example, screens and filters can be used to filter out sand and other particles before it can enter the pump. Yet, these device may eventually become plugged or may not prevent particles of a smaller size. A centrifugal separator is a more effective way to reduce the flow of sand and foreign particles that can reach the downhole pump.
As shown in FIGS. 1A-1B, casing 10 has perforations 12 toward a downhole end for entry of well fluids. A downhole pump 20 disposed in the casing 10 extends from a tubing string (not shown), which extends toward the surface. Extending from the pump 20, a centrifugal separator 30 is positioned near the perforations 12.
In FIG. 1A, the downhole pump 20 is a reciprocating rod-type pump for lifting liquid in tubing uphole to the surface. In this arrangement, the separator 30 mounts to the intake 22 of the pump 20 with tubing 16 and connector 18. As is known, such a pump 20 typically has a barrel in which a plunger can reciprocate by a sucker rod string extending from surface equipment.
In FIG. 1B, the downhole pump 20 is an electric submersible pump for lifting liquid in tubing uphole to the surface. In this arrangement, the separator 30 mounts downhole from the pump 20 using a packer 17, tubular housing 16, and the like. As is known, such a submersible pump 20 typically has a pump unit 21a driven by an electric motor 21b supplied with electrical energy from an electrical cable 21c extending from the surface. The packer 17 is positioned on the tubing 16 between the separator 30 and the pump 20. Production fluids are diverted into the separator 30, back into the casing 10 uphole of the packer 17, past the motor 21b for cooling, and into the pump intake 22.
In both of these arrangements, sand 15 in the well fluids from the adjacent formation enters the casing 10 through the perforations 12. To remove the sand 15 and other particles from the well fluid before it reaches the pump 20, the separator 30 first intakes the well fluid from the perforations 12 and separates the heavier solid sand and particles from the fluid before the pump 20 lifts the fluid through the tubing string.
Below the centrifugal separator 30, the assembly has a collector 40 with one or more mud anchor joints 40 that form a collection volume for solid particles from the separator 30. A bull plug 44 can plug the end of joints 42. The collector 40 collects sand and other solid particles and may be of a substantial length (e.g., thirty to three hundred feet). Instead of a bull plug 44, the collector 40 can have a dump valve to dump solids into the lower rathole on each downstroke of the pump 20.
As an example, FIG. 2A shows a centrifugal separator 30 for separating solid particles from the well fluid in the wellbore. The separator 30 is similar to that disclosed in U.S. Pat. No. 5,314,018.
A gas anchor body 34 connects to the tubing 16 with a connection 18a. The body 34 has inlet ports 32 for the well fluid flow to enter. The anchor body 34 connects to a desander body 35 with a connection 18b. The desander body 35 has a connection 18c that connects to a collector 40 having mud anchor joints 42 and bull plug 44. An orifice tube 36 extends down through the anchor body 34 to the desander body 35 and has a spiral head 38 on its distal end.
As noted above, such a centrifugal separator 30 is a preferred device for removing solids from the well fluid before it is pulled into the intake of the downhole pump 20. Produced fluids WF enter the separator 30 through the inlet slots 32 and flows down into the desander body 35 and through the spiral 38 to enter the orifice tube 36 and flow upward to the pump (20). The spiral 38 makes the flow follow a circular path through a “spiral-shaped” annular space. Details of the spiral on the orifice tube and the flow of fluid are shown in more detail in FIG. 2B. Through centrifugal action, the heavier particles S are forcibly spun against the desander body 35 and settle into the collector 40. Meanwhile, cleaner fluid CF remains at or near the axis of the intake tube 36 concentric to the desander body 35, thus allowing this “clean” fluid CF to be pulled into the intake for the pump (20).
The spinning action of the heavier (and very hard/abrasive) sand S wears against and erodes the inner diameter of the desander body 35. This erosion occurs to the point where the lower section of the separator 30 comes apart and drops into the well. In particular, the section of the desander body 35 at about the location of the spiral 38 parts, and the section of the body 35 along with the connected mud anchor joints 42 and the bull plug 44 drop into the well.
To address the issue of the separator coming apart, it is known in the art to incorporate milled flats on the outer diameter of the desander body. An example of such a separator is disclosed in U.S. Pat. No. 5,810,081, which is reproduced in FIG. 3. A milled flat 38 is made in an outer tubular member 20 of a separator 18. The milled flat 38 essentially reduces the wall thickness in the eroding section of the tubular member 20 near a spiral 32. During use, the reduced wall thickness eventually allows the sandy fluid to break through the tubular member 20 at 39 near a funnel 48. Once the fluid breaks through, the centrifugal spiral action stops, preventing the tubular member 20 from parting and keeping the lower section of the assembly from dropping into the well. This is effective, but reduces the life of the separator 18 and increases the production cost due to the machining operation required to mill the flats.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.